In the last twenty years there has been an active academic research in the domain of realizing digital logic functions (AND, OR, XOR, etc) by means of photonic devices. A main target application would be the realization of the desired all-optical computer, in which photons rather than electrons effect the interactions between the gates. In the last few years such efforts have been re-motivated by the desire to better exploit the high transmission capacity of optical communication network. This is envisioned to be achieved by all-optical networking, wherein the optical packets are routed by ultra-fast smart all-optical switches which interpret the headers and perform the switching functions, all in the optical domain, without involving conversion to electronics and back to optics. There has been some progress at the device level, using various approaches, most of which are based on one of the mechanisms: Cross-Gain Modulation (XGM) [1-5], Cross-Phase Modulation (XPM) [6-7], Four-Wave Mixing (FWM) [8-9] and Cross-Polarization Modulation (XPolM) [10-11]. These mechanisms usually depend on nonlinear effects in a Semiconductor Optical Amplifier (SOA). Other approaches based on Highly NonLinear Fiber (HNLF) were also proposed [12-13]. The XPM and XGM mechanisms inevitably limit the operating speed of such devices due to the carrier recovery time of SOA, where the FWM mechanism, which occurs on femtosecond timescales in SOA, is polarization sensitive and its related power penalty is an evident disadvantage. As for most fiber-based devices, their bulky size and poor power efficiency hinder their practicality.
In general, the desirable properties of all-optical logic devices would be:                Small Size—Efficient real-estate for Large-Scale Integration;        Ultra-Fast—Orders-of-magnitude faster than today's electronic gates (i.e., 40 Gb/s and above);        Low-Power dissipation;        Logic level restoration;        Cascadable—ability to interconnect and fan-in/out to form large logic arrays amenable to LSI (Initially hundreds of optical-transistors); and        Manufacturable—reliably and repeatably fabricated at low cost.General Background May Be Found in the Following Bibliography            [1] Sharaiha, A.; Li, H. W.; Marchese, F.; Le Bihan, J., “All-optical logic NOR gate using a semiconductor laser amplifier,” Electronics Letters, vol. 33, no. 4, pp. 323-325, 13 Feb. 1997    [2] Jae Hun Kim; Young Min Jhon; Young Tae Byun; Seok Lee; Deok Ha Woo; Sun Ho Kim, “All-optical XOR gate using semiconductor optical amplifiers without additional input beam,” Photonics Technology Letters, IEEE, vol. 14, no. 10, pp. 1436-1438, October 2002    [3]H. Dong, Q. Wang, G. Zhu, J. Jaques, A. B. Piccirilli, N. K. Dutta, Demonstration of all-optical logic OR gate using semiconductor optical amplifier-delayed interferometer, Optics Communications, Volume 242, Issues 4-6, 8 Dec. 2004, Pages 479-485.    [4] Kim, S. H.; Kim, J. H.; Choi, J. W.; Byun, Y. T.; Jhon, Y. M.; Lee, S.; Woo, D. H., “All-optical NAND gate using cross gain modulation in semiconductor optical amplifiers,” Quantum Electronics and Laser Science Conference, 2005. QELS '05, vol. 2, no., pp. 957-959 Vol. 2, 22-27 May 2005    [5] Ammar Sharaiha, Joseph Topomondzo, Pascal Morel, “All-optical logic AND-NOR gate with three inputs based on cross-gain modulation in a semiconductor optical amplifier”, Optics Communications Volume 265, Issue 1, 1 Sep. 2006, Pages 322-325    [6] Fjelde, T.; Wolfson, D.; Kloch, A.; Dagens, B.; Coquelin, A.; Guillemot, I.; Gaborit, F.; Poingt, F.; Renaud, M., “Demonstration of 20 Gbit/s all-optical logic XOR in integrated SOA-based interferometric wavelength converter,” Electronics Letters, vol. 36, no. 22, pp. 1863-1864, 26 Oct. 2000    [7] Webb, R. P.; Manning, R. J.; Maxwell, G. D.; Poustie, A. J., “40 Gbit/s all-optical XOR gate based on hybrid-integrated Mach-Zehnder interferometer,” Electronics Letters, vol. 39, no. 1, pp. 79-81, 9 Jan. 2003    [8] Kit Chan; Chun-Kit Chan; Lian Kuan Chen; F. Tong, “Demonstration of 20-Gb/s all-optical XOR gate by four-wave mixing in semiconductor optical amplifier with RZ-DPSK modulated inputs,” Photonics Technology Letters, IEEE, vol. 16, no. 3, pp. 897-899, March 2004    [9] Zhihong Li; Guifang Li, “Ultrahigh-speed reconfigurable logic gates based on four-wave mixing in a semiconductor optical amplifier,” Photonics Technology Letters, IEEE, vol. 18, no. 12, pp. 1341-1343, June 2006    [10] Soto, H.; Diaz, C. A.; Topomondzo, J.; Erasme, D.; Schares, L.; Guekos, G., “All-optical AND gate implementation using cross-polarization modulation in a semiconductor optical amplifier,” Photonics Technology Letters, IEEE, vol. 14, no. 4, pp. 498-500, April 2002    [11] Soto H., Topomondzo J. D., Erasme D., Castro M., “All-optical NOR gates with two and three input logic signals based on cross-polarization modulation in a semiconductor optical amplifier”, Optics Communications, volume 218, 1 Apr. 2003, pp. 243-247 (5)    [12] Yu, C.; Christen, L.; Luo, T.; Wang, Y.; Pan, Z.; Yan, L.-S.; Willner, A. E., “All-optical XOR gate based on Kerr effect in single highly-nonlinear fiber,” Lasers and Electro-Optics, 2004. (CLEO). Conference on, vol. 2, no., pp. 3 pp. vol. 2-, 16-21 May 2004    [13] Lee, J. H.; Nagashima, T.; Hasegawa, T.; Ohara, S.; Sugimoto, N.; Kikuchi, K., “40 Gbit/s XOR and AND gates using polarisation switching within 1 m-long bismuth oxide-based nonlinear fibre,” Electronics Letters, vol. 41, no. 19, pp. 1074-1075, 15 Sep. 2005    [14] Hinton, K.; Farrell, P. M.; Tucker, R. S., “The Photonic Bottleneck,” Optical Fiber Communication and the National Fiber Optic Engineers Conference, 2007. OFC/NFOEC 2007. Conference on, vol., no., pp. 1-3, 25-29 Mar. 2007